1. Field of the Invention
This invention relates to compositions for improving the flowability of aqueous coal suspensions, and a method for the use of such compositions.
2. Statement of the Related Art
Flowable aqueous coal suspension suitable for being transported through a pipeline must have viscosities of less than 1,000 cP at shear velocities between 10 and 200 s.sup.-1. At the same time, economic factors require a suspended coal solids content which is as high as possible. The coal contents of aqueous additive-free coal suspensions (depending on the properties of the types of coal employed) amount to a maximum to 55% by weight, since higher coal proportions result in viscosity increases and eventually in the loss of flowability. It has been known that additives containing surface active agents (tensides) and/or polymers cause the viscosity to be reduced and the flowability to be improved, thus making possible higher coal contents in the suspension.
U.S. Pat. No. 4,282,006 discloses aqueous coal slurries having coal contents of at least 60% by weight which contain an additive composition consisting of an anionic surfactant (e.g. naphthalene sulfonates, one example of which is "Lomar D") and an electrolyte (e.g. NaOH). The viscosities of the sus-pensions at 60 rpm are between 300 and 4,000 cP (aqueous Black Mesa mine coal slurry) and between 200 and 2,400 cP (aqueous West Virginia mine coal slurry).
Published Japanese patent application No. 56/57,891 describes aqueous coal slurries having coal contents of 60% by weight which contain maleic acid/acrylic acid copolymers in a concentration of 1% by weight as an additive. At an average copolymer molecular weight of 4,000, the viscosity is 1,800 cP.
Published European patent application No. 109,740 discloses aqueous coal suspensions having coal contents between 30 and 90% by weight, which contain propylene oxide/ethylene oxide block copolymer condensates of aliphatic or aromatic alcohols. The suspensions containing the polymers (independently of the coal properties) have lower viscosities than those suspensions wherein the block polymer has been replaced by sodium or calcium lignin sulfonates.
Published Japanese patent application No. 58/122,991 describes a mixture of glycerol-ethylene oxide/propylene oxide block polymer ether and tenside (e.g. sodium naphthalene sulphonate) which is added to coal suspensions having coal contents of from 50 to 80% by weight. The stability-life of the obtained suspensions was more than 4 weeks.
U.S. Pat. No. 4,441,888 describes the viscosity reduction of coal slurries using maleic acid/olefin copolymer salts, particularly the sodium salt of a maleic acid/C.sub.3-12 olefin copolymer. The specifically named copolymers are pentene sodium maleate and diisobutylene sodium maleate.